Packing element

ABSTRACT

Packing elements of the Pall ring type having improved resistance to crushing even though made from thinner gauge metal can be obtained by providing attachment means that hold overlapping ends of the ring together and resist deformation.

BACKGROUND OF THE INVENTION

This invention relates to packing elements use in mass transfer anddirect heat transfer applications and specifically to packing elementsof a generally cylindrical shape, such as for example Pall rings.

Such elements are used in reactors where liquids and gases are contactedso as to bring about a reaction, heat transfer, solution or dissolutionoperations by intimately contacting two flowing fluids. As a consequencethey have shapes designed to maximize surface area while retainingdimensional stability such they they do not collapse or become crushedduring use. One means of achieving this end is to form the rings fromcylindrical metal blanks, and providing internal structure by a varietyof suitable techniques.

It is however desirable to have a structure that is easily produced to astandard design in large volumes. To satisfy these requirements theelements are often stamped out of a flat metal plate intended to be bentinto a cylindrical shape with a plurality of flaps cut from the plateand bent inwards towards the axis of the cylinder. This is the shape ofthe typical Pall ring and is described for example in Reissue U.S. Pat.No. 27,217.

In order to retain the rigidity of such a ring it needs to be shapedfrom a relatively thick metal plate that will have be able to withstandthe compressive forces encountered in use. Lacking such rigidity therings will become compressed under the loading in the tower and morerings will be needed to fill the tower. In addition compressed rings donot have the same performance characteristics such that somepredictability in operation is lost.

On the other hand it is desirable to reduce the thickness of this metalplate to save weight and to make the rings less expensive.

One solution has been to use a pair of bridging members to hold twocooperating semicylindrical pieces together as is described in U.S. Pat.No. 4,197,264. This has a significant disadvantage in that theproduction process requires the combination of four separate componentsto make the final product.

The present invention provides a relatively rigid packing of the Pallring type while allowing the use of thinner gauge metal. The ringstructure is so designed that it can be made from a single strip ofmetal in a simple cutting and bending operation readily adapted to theuse of mass production techniques.

DESCRIPTION OF THE INVENTION

The present invention provides a packing element formed by bending aflat metal strip into a generally cylindrical form wherein overlappingends of the bent strip are provided with attachment means whichreleasably engage to hold the ends together when the ends areoverlapped.

The attachment means can have any convenient form but a generallyadaptable and advantageous attachment means comprises flaps bentinwardly towards the axis of the cylinder in the area of overlap of theends of the strip and the cooperating slots formed by the cutting of theflaps, with one end bearing a flap projecting away from the said end andthe opposed end having a flap in the area of overlap projecting towardsthe said end such that the flap projecting backwards fits into the slotformed by the cutting of the forward projecting flap. The flap can haveany convenient shape such triangular or rectangular but a simple,rectangular shape is often all that is required. Its length should beadequate to prevent unintended disengagement during use but not so longas to require extensive deformation of the cylinder to engage anddisengage. The cooperating flaps are preferably located at the midpointof the ends in the axial direction and generally one pair is enough. Itis however possible to employ two or more cooperating pairs to giveadded stability.

Such packing rings have a rigidity that greatly exceeds that of theprior art rings without the attachment means. This rigidity can befurther enhanced by providing the rings with peripheral flanges formedon the longitudinal edges of the metal strip such that, in the packingring, the flanges will be formed around the top and bottom ends of therings. The flanges preferably project in such a direction the will notimpede the bending of the strip into a ring shape. Thus in the finishedring the flanges project radially outwards rather than inwards. One ofthe flanges preferably terminates short of the ends of the strip suchthat the flanges do not contact when the attachment means are engagedbut permit a limited degree of flexing of the ring before they come intocontact. This contact limits the amount of deformation that can occur innormal use and renders the ring quite rigid. The flange however does notprevent disengagement of the preferred attachment means, (comprisingflap and cooperating slot), which can be released by deforming theoverlapped end inwards, (but not the overlapping end), so as todisengage the flap from the cooperating slot.

The metal from which such rings are made is largely dictated by theenvironment in which it is designed to be used. Since this is oftencorrosive to some degree, it is conventional to use a resistant steelsuch as stainless steel, which is usually costly.

The gauge of the metal strip from which a Pall ring or similar structureis conventionally constructed is from about 0.65 mm to 1.00 mm and moretypically from about 0.75 mm to about 0.85 mm. The improved packing ringstructure of the present invention allows the use of metal strip ofgauge down to about 0.10 mm and preferred packing ring structures areconstructed from metal strips of 0.15 mm to 0.60 mm gauge.

The conventional Pall ring structures are cylinders formed from a bentstrip of metal and are provided with a plurality of inward flapprojections cut from the bent strip and arcing inwardly toward the axisof the cylinder but terminating short of the axis. The number and sizeof these projections is not critical and is largely a function of thedimensions of the ring and the desired surface area. The provision ofsuch projections is also a desirable feature of the packing rings of thepresent invention.

Initial test data indicate that the rings according to the presentinvention can support up to 950 lb/ft² which is about equal to thesupportable load for a ring of the same dimensions, made from steelstrip that is 50% thicker, but which lacks the attachment means thatcharacterizes the rings of the present invention. This means that deepertower beds of packing can be employed without the need for intermediatesupport structures to avoid crushing the rings in the lower portions ofthe tower. In addition the use of thinner gauge steel leads tosignificant cost advantages for the structure of the present invention.

DRAWINGS

The attached drawings are described as follows:

FIG. 1 is a longitudinal cross-section of a metal strip before it isbent into a cylindrical shape showing the attachment means.

FIG. 2 is side view of a Pall ring having the structure of the presentinvention.

FIG. 3 is a cross-section of the ring shown in FIG. 2 in along the line2--2.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention will now be further described with specific reference tothe embodiment illustrated in the Drawings which are for illustrationonly and are intended to imply no limitation on the essential scope ofthe invention.

In the Drawings, and referring initially to FIG. 1, a metal strip, 1, isprovided at each of its extremities with flaps, 2, punched out of thestrip to leave slots, 4. The strip is also provide with flanges, 3,along the longitudinal edges terminating short of the end of the strip.

FIG. 2 shows the strip of FIG. 1 bent to form a cylindrical structurewith one end overlapping the opposed end such that the flap on theoverlapping end engages the slot on the end beneath the overlapping endand the tendency of the strip to straighten holds the ends in lockingrelationship with the flaps on opposed ends in contact.

FIG. 2 also shows a flexing space, 6, between the flanges on opposedends of the strip. This allows the ends to increase the degree ofoverlap slightly so as to permit engagement and disengagement of theflaps and slots that comprise the attachment means but resist anyfurther deformation when the flange ends come into contact.

FIG. 2 also shows the inwardly directed projections, 5, that are stampedfrom the sheet and are deformed inwardly towards the axis of thecylinder, usually after the cylinder has been formed. Typically thereare from four to eight such projections arranged in the same planeperpendicular to the axis of the cylinder. The preferred embodimentshown in FIGS. 2 and 3 has two sets of five projections arranged in twoplanes, one above the plane of the attachment means and one below theplane of the attachment means.

FIG. 3 is a cross-section along the plane 2--2 in FIG. 2 and is designedto show in detail the interaction of the flaps 2, with the slots, 4, toform the attachment means.

The attachment means shown in the above drawings could be replaced withother structures capable of performing the same task such as theformation of curls of opposite sense, (that is, one up and one down), onthe ends of the strip so as to permit engagement of the curled portionswhen the ring is formed. Packing rings with other interlocking means toachieve the same objective could be devised and all such are understoodto be within the purview of this invention.

I claim:
 1. A packing element formed by bending a metal strip into a generally cylindrical shape with overlapping ends, said ends being provided with attachment means which releasably engage to hold the ends together when overlapped, wherein the attachment means comprises at least one pair of flaps projecting from the plane of the strip at essentially the same angle and in the same direction, with each flap located adjacent an end of the strip in the region of overlap when the element is formed, and at least one cooperating slot adjacent one of the flaps such that the flap formed on the opposed end engages with the slot when the element is formed.
 2. A packing element according to claim 1 in which the attachment means comprises at least one pair of flaps stamped out of the strip and projecting from the plane of the strip at essentially the same angle and in the same direction, with each flap located adjacent an end of the strip in the region of overlap when the element is formed, and cooperating slots formed when the flaps are produced, such that the flap on one end engages with the cooperating slot on the other end.
 3. A packing element according to claim 1 having two or more attachment means.
 4. A packing element according to claim 1 in which the cylinder ends are provided with flanges which act to limit the degree of overlap of the ends of the strip from which the cylindrical element was formed.
 5. A packing element according to claim 1 in which a plurality of projections are provided extending from the cylinder wall and generally towards the axis of the cylinder.
 6. A packing element according to claim 1 in which the element is stamped from a strip of metal from 0.10 to 0.60 mm in thickness. 